1. Field of the Invention
The present invention relates to an improvement in a method for analyzing the creep characteristic of a plastic molded substance.
2. Description of the Related Art
Conventional methods for analyzing creep characteristic of various molded substances are known wherein the creep characteristic is calculated by a finite element method based on a model such as a power multiple law or hyperbola law.
For example, described in Japanese Patent Laid-Open Publication No. Hei 11-166884 is an analysis method of a bending creep characteristic of a plastic molded substance in which the following Nutting""s formula, being one of the power multiple laws, is employed.
dxcex5cr/dt=A"sgr"ntmxe2x80x83xe2x80x83(1)
In this equation, xcex5cr represents creep strain, "sgr" represents stress, t represents elapsed time, and A, n, and m respectively represent constants defined by the material.
However, in the above conventional method for analyzing creep characteristic of a plastic molded substance, the same creep characteristic value, such as, for example, one set of creep characteristic value obtained from a bending test, is assigned to all the sections of the plastic molded substance, which is the analysis target. There therefore remains a problem that the creep characteristic cannot be precisely analyzed. This results from the fact that there are various shapes for the plastic molded substance, which is the analysis target, and hence, various stress conditions for each section of the plastic molded substance having different shapes or fastening conditions. Because creep characteristic values vary greatly according to the stress condition, assigning the same creep characteristic value to all of the sections results in inherently inaccurate estimates.
The present invention is conceived to solve the above problem, and one object of the present invention is to provide a creep characteristic analysis method for a plastic molded substance wherein the creep characteristic of an actual resin molded substance having various stress conditions due to different shapes or fastening conditions can be precisely analyzed.
In order to achieve at least the object above, according to one aspect of the present invention, provided is a method for analyzing creep characteristic of a plastic molded substance comprising the steps of calculating stress values for a substance or each section of a substance; determining stress condition at each section to be tensile or compressive based on the stress value; assigning a creep characteristic value to each section based on the determination result; and analyzing the creep characteristic after a predetermined time has elapsed using the creep characteristic values.
In the above method for analyzing creep characteristic of a plastic molded substance, it is preferable that the analysis result of the creep characteristic is reflected on the determination of the constraint condition or shape of the plastic molded substance.
In the above methods for analyzing creep characteristic of a plastic molded substance, it may also be preferable that the stress condition be determined to be tensile stress when the hydrostatic stress value is positive and the stress condition is determined to be compressive hydrostatic stress when the stress value is negative.
The method for analyzing creep characteristic of a plastic molded substance may be preferably applied to a finite element method.